Control means for series connected cylinder drive assemblies



Aug. 11, 1964 E. w. PEARSON ETAL 3,

CONTROL MEANS FOR SERIES CONNECTED CYLINDER DRIVE ASSEMBLIES Filed July 17, 1962 2 Sheets-Sheet 1 IN VEN TORS Z63 EUGENE (PEARSON HOLLAND AR/CHARDSO/V BY THE/l? ATTORNEYS Aug. 11, 1964 E. W. PEARSON ETAL CONTROL MEANS FOR SERIES CONNECTED CYLINDER DRIVE ASSEMBLIES Filed July 17, 1962 2 Sheets-Sheet 2 K 53 I CONVEA/T/ONAL FULL I M Q L040 cum 5 l-- :.---i

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LOAD LOCATION United States Patent Office? 3,143,924 Patented Aug. 11, 1964 CONTROL MEANS FOR SERIES CONNECTED CYLINDER DRIV E ASSELIES Eugene W. Pearson, Orinda, and Rolland A. Richardson,

Alameda, Calif, assignors to Pacific Industrial Manufacturing Co., a corporation of California Filed July 17, 1962, Ser. No. 210,489

16 Claims. ((11. 91-471) Our invention broadly relates to hydraulic cylinder drives employing a plurality of cylinder drive assemblies in series, and more particularly relates to control means for accurately synchronizing the piston movements of two or more of such cylinder drive assemblies when hydraulically connected in series.

The invention, however, will be described specifically from the viewpoint of its application to a press brake hy- .draulically powered by series connected cylinder drive assemblies, where the invention serves a real need. Fol- .lowing an understanding of the invention, it will become apparent that the principles involved are applicable to other and widely diversified situations and equipment such as missile or rocket platforms, diving vanes for submarines, etc.

.Among the objects of our invention are:

(1) To provide novel and improved control means for a hydraulic drive system employing a plurality of cylinder drive assembliesconnected in series;

(2) To provide novel and improved control means for a plurality of cylinder drive assemblies in series, which control means can be utilized to maintain a fixed relationship between the travel of the pistons of said plurality of cylinder drive assemblies;

(3) To provide novel and improved control means for a plurality of cylinder drive assemblies in series, which control means will serve to limit the maximum load capable of being placed on any one of the cylinder drive assemblies and their supporting structure;

(4) To provide novel and improved control means for a plurality of cylinder drive assemblies in series, which means will effectively relate the stroke terminating position of one piston to that of the other in the series;

(5) To provide noveland improved control means for a hydraulically powered machine having a reciprocating ram or platen and series connected cylinder drive assemblies for driving said ram or platen;

(6) To provide novel and improved control means for a hydraulically powered machine having a reciprocating ram or platen and series connected cylinder drive assemblies for driving said ram or platen, said control means serving to maintain a fixed relationship between the pistons of the respective cylinder drive assemblies;

(7) To provide novel and improved control means for a hydraulically powered machine having a reciprocating ram or platen and series connected cylinder drive assemblies for driving said ram or platen, said control means permitting accurate control of the stroke of said ram or platen;

-(8) To provide novel and improved control means for a hydraulically powered press brake or the like having a reciprocating ram or platen and series connected cylinder drive assemblies for driving said ram or platen, said control means making it possible to limit the maximum permissible force on each piston of said series connected drive assemblies.

Additional objects of our invention will be brought out in the following description of a preferred embodiment of the .same taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a view depicting applicants invention as applied to a press brake;

FIGURES 2a, 2b, and 2c depict by means of diagrams,

the development of the loading characteristics attributable to the present invention.

In connection with certain of the features of the present invention, it is imperative that one distinguishes between a press brake to which these features are pertinent, and a hydraulically driven shear wherein the particular problems involved in the press brake, are not present.

For example, in the functioning of a shear, the entire load is concentrated at the point of contact between the upper blade and the work, and in shearing through a sheet of metal or the like, the load on the machine will start at one edge of the sheet, which will be close to or under one of the drive cylinder assemblies, and move across the work to the opposite edge of the sheet, which may terminate adjacent to or under the other cylinder drive assembly.

This is a typical load characteristic of a shear, and inasmuch as the full rated load of the machine may start under one of the cylinder drive assemblies, and, or terinate under the other drive assembly, the machine side ousings or supports for the upper blade must be designed to withstand the full rated load capacity of the machine. Because of this, a shear lends itself to the application of a series of hydraulic system to drive the same, and such a system, being quite simple in its layout and under ideal conditions, inherently stable, its application to shears presents no grave problems and has its advantages.

In a press brake, on the other hand, the ram functions to deform a sheet of metal between two cooperating dies, and accordingly, the loading on the machine, once the work is positioned, is stationary, and does not, as a rule, travel from the region of one drive assembly toward that of the other drive assembly as is the case with the shear.

In using a press brake, an operator normally places the work at or close to a position under the center of the ram, or in other words, at a location of symmetry with respect to the cylinder drive assemblies. Under these conditions, neither side housing is called upon to withstand the strains and stresses of more than half the full rated load capacity of the machine. Consequently, the side housings or supporting frame structure of a press brake need not be rugged enough to withstand the full rated load value of the machine, as is required of a shear.

It would be uneconomical, therefore, to construct a machine of the press brake type wherein the side housings or supporting frame are designed to withstand the full rated load of the machine when such supporting structure, in normal use, is not required to be exposed to such strains or stresses. Yet, it is desirable to hydraulically drive the ram of such machine through cylinder drive assemblies connected in series, as in a shear, because of the advantages of such system, but, unfortunately a series drive system does not inherently lend itself to driving a press brake, without exposing one or the other of the side housings or other supporting structure to full rated load stresses and strains should the work be positioned toward or beneath either of the drive assemblies.

Referring to the drawings for details of our invention as applied to a press brake, the press brake is schematically shown as involving a pair of side housings 1 and 3, constituting the main portion of the supporting frame of the machine, such side housings being spanned across the lower front edges thereof by a wall or bed 5 for supporting the lower die '(not illustrated) of the press brake.

Above and in the plane of the bed 5 is the ram 7 which is slidably mounted on the front edges of the side housings, for reicprocal drive movement-by a pair of cylinder drive assemblies 9 and 11, each supported by one of the side housings at a point above the ram. The ram is adapted to carry a die (not illustrated) along its lower edge for cooperation with the first die to deform metal positioned between the two cooperating dies.

The cylinder drive assembly includes a closed cylinder 15 housing a double acting piston 17 with a piston rod 19 extending therefrom and pivotally secured to the proximate upper corner of the ram 7.

Similarly the cylinder drive assembly 11 includes a closed cylinder 23 housing a double acting piston 25,

which has a piston rod 27 extending therefrom and pivotally connecting to the proximate upper corner of the ram 7.

These drive assemblies are connected in series in a hydraulic drive circuit comprising a main pump 31 having a suction line 33 terminating in a supply tank 35, the discharge line 37 of the pump connecting to a port in a solenoid operated reversing valve assembly 411 having an intermediate or neutral section 43 which conveys the pump discharge back to the supply tank 35. A flow line '47 connects from another port in said reversing valve assembly, to the upper end of the cylinder 15 of the drive assembly 9, above the piston 17 to convey fluid under pressure to such cylinder for a down or work stroke of the ram. An intermediate fiow line 49 couples the said same cylinder from a point below the piston, to

the top side of the other cylinder 23 of the drive assembly 11, while a return flow line 53 from a point below the second piston 25 connects with another port in the reversing valve assembly 41.

The first cylinder drive assembly 9 is of greater size than the other, such that the surface area of the under side of its included piston 17 equals the area of the top side of the piston 25 in the other cylinder drive assembly 11. By reason of this area relationship, the drive system will under ideal conditions, maintain a relative rate of feed of liquid to the drive assemblies, such as will produce equal rate of travel of the pistons and resulting uniform linear movement at both ends of the ram.

A check valve 57 in the return line, is spring loaded sufiiciently to support the ram in its uppermost position. Because of this, a basic pressure will prevail in the hy draulic system. This basic pressure, however, is of little relevance to the present invention.

In one position of the reversing valve assembly 41, liquid flow in the hydraulic system will be in a direction to produce a down or work stroke, while in the opposite position of the reversing valve assembly, the flow in the hydraulic system will be reversed to produce an up stroke. In order to eifect such an up stroke, the ram supporting check valve 57 in the return line, must be by-passed by a check valve 61, spring loaded in the reverse direction.

By reason of the fact that the larger cylinder drive assembly 9 controls the functioning of the other cylinder drive assembly 11, the first assembly may be designated the master assembly, and the other cylinder drive assembly will then be designated the sleeve assembly.

The foregoing series hydraulic system represents a conventional hydraulic system with the cylinder drive assembly in series, except for the fact that it does not depict the presence of an overload relief valve normally included in the system when installed in a shear, where it would be set at the full rated load of the machine and connected in a flow line from the pump discharge line back to the supply tank.

With such relief valve in the system, it can be shown that the force topside of the slave piston is equal to 11/ P1 where P1 represents the force topside of the master piston, letter b represents the linear distance from the center of the work, to the master piston 17 and the letter I represents the linear distance between the pistons 17 and 25.

Based on this relationship, the apportionment of a resulting work load as the work is moved from a location beneath the slave piston 25 to a position beneath ,ieaass the master piston 17, is depicted in the curves of FIG. 2a to which reference will now be made.

As the work is shifted from the position beneath the slave piston 25, the portion of the load taken by the slave piston, as represented by the dotted line curve 67-, gradually diminishes from full load value and drops to base pressure as the work reaches a position beneath the master piston. Conversely, that portion of the load taken by the master piston 17, as represented by the dotted line curve 69, will start at the basic pressure when the load is under the slave piston, and end up with maximum full rated load, when the work reaches a position beneath the master piston.

Totalling the load carried by both pistons at any location of the work, will show that the total load remains substantially constant, and is represented in FIG. 2a by the horizontal dash line 71, which is not what one would want in a press brake or like machine.

The desired maximum permissible load curve for a press brake or like machine, due to the fact that the work,

in the normal use of such machine, is placed substantially symmetrical to the two drive cylinder assemblies, would be a curve 72 wherein the full rated load capacity of the machine can be handled in a normal manner, with the location of the work centrally of the ram, and with limitations built into the machine which would diminish the maximum permissible loading of the machine as the work is shifted toward one or the other end of the ram, with the loading under either one of the pistons limited to a maximum permissible value of substantially half the full rated value of the machine.

As one step toward arriving at such load characteristic, we provide a flow connection 73 from the supply line 47 to the supply tank 35, and in such flow connection, we locate a relief valve 74 which is set to open at the maximum force permissible against the slave piston 25, and we control its operation from the flow line 49 or its equivalent, and the lower end of the master piston 15, by a pressure connection 75.

With such relief valve in the system, the load characteristic attributable to the slave piston will change from that of the curve 67 of FIGURE 2a to that of the dotted line curve 77 of FIGURE 2b, in accordance with which, it will be noted that the maximum permissible force that could build up against the slave piston will drop from full rated load capacity of the machine to approximately half such load value, and will continue at such value as the work is moved to a location centrally of the ram, at which point, the curve takes on the normal characteristic of that of FIGURE 2a, as the location of the work is shifted further toward a position under the master piston 17.

As for the portion of the load taken by the master piston, it will be noted by an examination of the curve 7 9 of FIGURE 2b, that the introduction of the relief valve 74 in the connection 73 from the flow line 49 between the cylinder drive assemblies has no eflFect on the load taken by the master piston.

Totalling the load values represented by the aforementioned curves 77 and 79, the total load characteristic of the machine will follow the combination dot-dash and dash line curve 81 of FIGURE 2b, wherein the values represented by the dash portion will correspond to the rated full load value of the machine as in FIGURE 2a, while the dot-dash portion represents a drop in the maximum permissible load on the machine, as the work approaches a position under the slave piston.

Because of the series nature of the hydraulic system which powers the machine, a similar relief valve bearing the same setting value and the same relationship to the master cylinder drive assembly as the relief valve 74 bears to the slave cylinder drive assembly, will not convert the curve 81 to the final desired load characteristic curve 72 of FIGURE 2a, as one might offhand think would be the result. Were such relief valve installed, the full load capacity of the machine would be cut in half for all positions of the work, and the effect would be the same as lowering the horizontal dash curve 71 of FIGURE 2a to a point representing approximately half that value.

We have solved this portion of the problem by provid- "inga by-pass flow connection 85 from the pump discharge line 37 .to the supply tank 35 and in this by-pass, We include an overloadrelief valve 87.

This overload relief valve assembly comprises a valve housing 91 providing a longitudinal valve chamber 93.

Slidably disposed in the valve chamber is a valve 95 hav- The valve housing is provided with two main ports, one 103 being normally blocked by the valve in the closing position of the valve, but exposing the perforation 1M in such valve position; and the other port 105 exposing to tank '35, the valve chamber about the valve stem 97 between the valve 95 and the piston 99.

A compression spring 107 installed under compression with one end in the valve recess and the other end against the proximate end of the housing, serves, in the absence of other factors, to bias the valve 95 to its illustrated closing position.

The pump end of the by-pass line 85 connects with the valve assembly housing at the port 103, while the supply tank end is coupled to the port 105.

To open this overload relief valve assembly, the valve 95 must be urged in a direction against the biasing action of the spring 1&7. Pressure'in this direction is applied to the piston -99 via a bore 109 in the housing Wall from the port 163.

Closing the valve assembly housing 91 at the spring end and providing the abutting wall for the spring 1197, is a-pilot valve assembly 115 including a sub-housing 117 having a longitudinal chamber 119 with a flow connection at one end to the pump end of the by-pass connection 85, preferably by means of a bore 120 in the housing 91 and leading to the port 103.

Thus pump pressure will always be supplied to the main valve chamber'93 against the piston 99 as well as to one end of the pilot valve assembly chamber 119, where it will be applied against one end of a spool type pilot valve 121, against the other end of which bears a bias spring 123, adjustably compressed by an adjusting plug 127 which is threaded into the proximate end of the pilot valve housing.

Also prevailing pump pressure will build up by way of the perforation 101 against the spring engaged end of the valve, thus balancing the pressure being applied to the valve piston 99 and, in the absence of other factors, permitting the spring to retain the valve inits closedposition.

Through the wall of the pilot valve housing and coupling the proximate end of the main valve chamber with the pilot valve chamber at the region of a reduced section of the pilot valve 121, is a bore 131.

A flow connection 135 from the pilot valve chamber to the outlet port 105, through the wall of the main valve housing, is blocked by the pilot valve when in theposition illustrated, but such valve when shifted to the right is adapted to expose this latterflow connection to the bore 131 and thus provide for release of the pump pressure prevailing against the main valve in opposition to the pressure against the piston '99. Upon release of such pressure, the main valve will move to open position, to flow connect the outlet port 105 with the inlet port 193 and permit the output of the pump to go back directly to the supply tank and by-pass the series cylinder drive assemblies.

Supplementing the pressure of the pilot valve spring 123 is the hydraulic pressure developed in the flow line, such pressure being conveyed to the pilot valve by a pressure line fromthe flow line .to the pilot valve chamber at the spring end thereof, and identified by reference numeral 139.

Withsuch pressure connection installed, the spring adjustment is set to bring the overall adjustment of the relief valve assembly to the maximum full load rating of the machine. This will have no effect on the loading characteristics of the slave piston, but insofar as the loading on the master piston is concerned, it will have an effect, for as the position of work is shifted from a central position under the ram toward the end of the ram under the master piston, the resulting diminishing pressure in the flow line connecting the cylinder drive assemblies will decrease and correspondingly lower the overall pressure against the pilot valve of the relief valve assembly, and consequently correspondingly lower its adjustment .until the Work is positioned under the master .piston, at which point, the setting of the relief valve assembly will have dropped to approximately half the full load rating of the machine.

In lieu of the pilot operated relief valve just described, we could utilize a direct-acting relief valve, though we prefer the former.

'The result is a maximum load characteristic curve 141 for the machine, such as represented by the dot-dash curve of FIG. 20, wherein thepeak of the curve, occurring when the work is substantially centralized with respect to the cylinder drive assemblies, represents the full load rating of the machine. With a machine having a built in maximum load characteristic curve as shown in FIG. 20, it becomes apparent that the side housings or frame of the machine need no longer be constructedto withstand full load strains and stresses, and, therefore, can be lightened result in slight angular deviations of the ram, which effect can become cumulative if not quickly corrected.

The necessity for such correction in a press brake is of exceedingly great importance, since failure to do so, will result in the ram producing greater than desired deformation 'of Work at one end than at the opposite end,

and accordingly ruin such work. Such correction is effected instantaneously and accurately in accordance with the present invention.

Toward this end, we provide a valve assembly 151,

preferably one along the lines of the .valve assembly forming the subject matter of the pending application of Eugene W. Pearson for Precision Adjustable Control Valve Assembly,'Serial No. 111,547, filed May 22, 1961. Such valve assembly, as herein employed, involves a valve housing 153 with three ports 155, 157 and 159,

and a spool type valve 161 slidable within said housing and adapted in a symmetrical or neutral position, to block communication between one of said ports and either of the remaining ports 157 or 159. When moved in one direction the valve is adapted to flow connect said one port to port 157 when moved in the opposite direction from its neutral position, the spool type valve is adapted to flow communicate the said one port 155 with the remaining port 159, to the exclusion of the second port 157. The valve 161, at one end is biased in one direction by a spring 167, while at itsopposite end, the valve is connected by a stiff spring 169 to one end of a tapelike element or cable 171, which extends zigzag across the length of the ram, as determined by spaced sheaves and 177 on the back of the ram, and anchored at its other end to a bracket 179 on one of the side housings of the machine. The stiff spring 169 connecting the valve 161 to the end of the tape-like element or cable, is preloaded greater than the valve spring, and does not begin to elongate until its preload value is exceeded. It thus functions only in emergencies toprotect the valve '161.

The valve housing 153 is mounted on a fixed portion of the machine in such location that the valve element will respond and shift its position when the effective length of the tape is altered, as will occur should the ram angularly deviate in either direction from an assigned position.

The one port 155 of the housing is connected to the intermediate flow line 49 by a flow connection 185 while of the two remaining ports, one 157 is connected to the pump 31 by a control pilot line 187 in which is located a valve 189 of the check valve type, while the other port 159 is connected to the supply tank 35 by a flow connection 191.

With the valve 161 adjusted to its neutral position, and with the ram 7 in its desired position, which in a press brake will inevitably be horizontal, the condition of the valve will remain status quo until the ram, for some reason or other, should angularly deviate from its assigned position and produce an effective change in the length of the tape-like element which, in turn, will result in a shift of the valve 161 in one direction or the other, and either connect the pump 31 through the valve assembly to the flow line 49, to increase the supply of pressure liquid to the slave cylinder, or connect the flow line 49 to the supply tank 35, to diminish the supply to the slave cylinder, depending on whether hydraulic fluid must be added to or removed from the fiow line, to reestablish the ram to its previously or desired position.

A critical factor toward realizing prompt and exceedingly accurate corrections for such deviations, lies in the use of a valve assembly in which, in the neutral condition of the valve assemby, there is no overlap between the valving portions of the valve and the lands between the ports. In fact, a slight underlapping may be desirable.

Adjustment of the valve spool to its neutral position may be very conveniently effected by mounting one of the sheaves such as sheave 177, on one end of a pivoted lever 195 with the opposite end of the lever held in engagement with the end of an adjusting screw 199 by the pressure exerted by the tape-like element on such sheave. Accordingly, by adjusting the screw 199, the tape-like element may be effectively lengthened or shortened Sl11'fi ciently to effect the adjustment of the valve assembly.

With the valve assembly thus properly adjusted for the desired position of the ram, any tendency on the part of the ram to deviate angularly from its desired position, will initiate a correction operation by either bleeding liquid from the flow line between the two cylinder drive assemblies or adding liquid thereto, as the case may be. By such means, extreme accuracy of the order of 1000th of an inch has been realized in the operation of a press brake incorporating the features of the present invention.

As a protective measure against failure of the tape-like element, for any reason whatsoever, we take advantage of the construction of the valve assembly 151 to open an emergency circuit which will remove power from the machine. It will be noted that upon such failure, the biasing spring 167 associated with the valve, will be free to shift the valve to an extreme position, in which position, it may be made to strike a normally closed emergency switch 201 to open such emergency circuit.

The ability to maintain proper orientation of the ram in a press brake, in conjunction with control of the work stroke or travel of the ram is of paramount importance in realizing accuracy in the performance of the machine.

Control of the stroke of the ram is conventionally accomplished electrically through the utilization of limit switches in accordance with the teachings of the patent to Castle et al., for Press Brake, No. 2,558,071 of June 26, 1951, or the patent to Richardson, for Precision Control System for Press Brakes or the Like, No. 2,906,096, of Sept. 29, 1959.

In accordance with the present invention, control of the work stroke of the ram is accomplished hydraulically through utilization of the relief valve assembly 87 in common with the previously described system for limiting the maximum permissible load on the side housings of the machine.

In conjunction with such relief valve assembly, we accordingly, provide a valve assembly 215 of a type similar to the valve assembly 151, the valve assembly 215 being preferably bracket mounted to one of the side housings of the machine and in position along side the path of travel of the proximate end of the ram 7.

This valve assembly involves a valve housing 219 having a plurality of ports 221, 223, 225, 227 and 229, preferably five in number, with a spool type valve 231, such that in its up position, as determined by the bias spring 233, the valve assembly will flow connect the uppermost port 221 to the adjacent port 223, and the following port 225 to the port 227 below it, leaving the bottom port 229 blocked off. The valve 231 at its lower end, is provided with a stem 237 extending downwardly therefrom, and to the end of which is mounted an arm 239 extending into the path of travel of an adjustable stop 241 threadedly mounted in a bracket 243 extending laterally from the proximate end of the ram. During downward travel of the ram, the adjustable stop 241 will abut the arm 239 and shift the valve 231 downwardly against the action of its biasing spring 233, and in so doing, will flow connect the two lowermost ports 227 and 229, and likewise flow connect the two ports 223 and 225 above them, leaving port 221 blocked off.

The uppermost and lowermost ports 221 and 229 respectively, are connected to the supply tank 35, the second port 223 is connected by a fiow line 251, through a check valve 253 to a bore 255 in the housing 91 of the relief valve assembly and leading to the valve chamber below the piston 99. The third port 225 is connected by a line 257 to the output or discharge side of the pump 31 While the next port 227 is connected by the line 261 through a check valve 263 to a port 265 in the pilot valve assembly of the relief valve assembly, which has flow connection through the pilot valve chamber with the bore 131, which extends the flow path to the port 103 by way of the perforation 101 in the valve, and thus exposes this flow connection to the pressure side of the pump.

With the hydraulic connections as thus described, it will be apparent that, as the ram moves downward to perform a work stroke on Work placed in the machine, the stop 241 will ultimately engage the arm 239 and upon shifting the valve, the hydraulic pressure supplementing the spring 101 against the valve 95 will immediately be relieved to the tank 35, thus permitting the pump pressure against the valve piston 99 to predominate and lift the valve 95 off its seat, to flow connect the pump 31 directly to the supply tank 35 and thus remove the power from the machine and cause it to come to a quick stop. The stroke control valve assembly, being of an extremely sensitive type, can be made to bring the ram to a halt within a thousandth of an inch.

The return stroke of the ram is not so critical, and its upper limit of travel accordingly, may be determined hydraulically, electrically or mechanically in accordance withl any existing prior art means for accomplishing this resu t.

With the overload relief valve assembly 87 in the system, We could utilize the same in conjunction with an added pilot valve similar to that of the pilot valve to perform the function of the relief valve 74.

The term cylinder drive assemblies or equivalent terminology is to be construed to include rotary hydraulic drive means and not be limited to hydraulic drive assemblies where the movements of the pistons are linear only.

From the foregoing description of our invention, it will be apparent that the same fulfills all the objects thereof, and while we have illustrated and described the same in its preferred form and in considerable detail, the invention is subject to alteration and modification without departing from the underlying vprinciples involved, and accordingly, do not desire to be limited in our protection to such details as we have illustrated and described, except as may be necessitated by the appended claims.

We claim:

1. In combination a series hydraulic drive system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a flow line from said master drive assembly to said slavedrive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting the maximum permissible force on each of the pistons of said series connected drive assemblies, said means including,

a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of forceagainstthe slave piston, and

a pilotconnection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure valve corresponding to twice the maximum force permissible against said slave piston, and automatically reducing said adjustment to a pressure Value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a spring adjustment for said valve, and a pressure connection from said flow line to said relief valve and inpressure aiding relationship to the spring adjustment therein,

means for stabilizing a fixed relationship between the pistons of the respective cylinder drive assemblies, said means including,

mechanical means pivotally connected at each end to the pistons of said series connected cylinder drive assemblies,

a valve assembly having a port, flow connected to the flow line between said pair'of cylinder drive assemblies,

a port, flow connected to a source of pressure liquid,

a port, flow connected for discharge fromsaid flow line, and

means coupling said mechanical means and said valve assembly to counteract undersired angular deviations of said mechanical means from a desired position.

2. In combination a series hydraulic drive system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal toithe top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting the maximum permissible'force on each of the-pistons of said series connected drive assemblies, said means including a flow connection from pumppressure to discharge,

a pilot relief valve in said flow-connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposedto system pressure developed against said slave piston,

a 'flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value correspondingto twice the maximum force permissible against said slave piston and automatically reducing said adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including aspring adjustment for said valve, and apressure connection from said flow line to said'last mentioned relief valve and inpressure cooperative relationship to the spring adjustment in said relief valve, and

means for stabilizing a fixed relationship'between the pistons ,of the respective cylinder drive assemblies, said means including,

mechanical means pivotally connected at each end to the pistons of said series connected cylinder drive assemblies,

a valve assembly 'having aportfflow connected to the flow line between said pair-of cylinder drive assemblies,

a port, .flow connected to a source of pressure liquid,

a port, flow connected for discharge from said flow line,

and means responsive to angular deviations of said mechanical means in one direction from a desired position for adjusting said valve assembly to connect said first mentioned .port 'to the second mentioned port, and responsive to angular deviations 'in the reverse direction to connect said first mentioned port to said third mentioned port.

3. In combination a series hydraulic drive system comprising apair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston Whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow linefrom said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means forlimiting the maximum permissible force on each of the pistons of said series connected drive assemblies, said means including a flow connection from pump pressureto discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line,.to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value corresponding to twice the maximum force permissible against said slave piston and automatically reducing said adjustment to a pressure value corresponding to said maximum permissible slavepiston force, with changes in work position, from aposition of symmetrybetween said cylinder drive assemblies to a positionsubstantially beneath said master drive assembly,

said means including a spring adjustment for said valve, and a pressure connection from said flow line to said relief valve and in pressure aiding relationship to the spring adjustment therein,

means for stabilizing a fixed relationship between the pistons of the respective cylinder drive assemblies, said means including,

mechanical means pivotally connected at each end to the pistons of said series connected cylinder drive assemblies,

a valve assembly having a port, flow connected to the flow line between said pair of cylinder drive assemblies,

a port, flow connected to a source of pressure liquid,

a port, flow connected for discharge from said flow line,

and

means coupling said mechanical means and said valve assembly to counteract undesired angular deviations of said mechanical means from a desired position, and

means for hydraulically limiting the stroke of said pistons.

4. In combination 7 a series hydraulic drive system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting the maximum permissible force on each of the pistons of said series connected cylinder drive assemblies, said means including a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

and

means for adjusting said last mentioned relief valve to a pressure value corresponding to twice the maximum force permissible against said slave piston and automatically reducing said adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position,

from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly.

5. In combination a series hydraulic drive system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting maximum force against each of the pistons of said series connected cylinder drive assemblies, said means including a flow connection from pump pressure to discharge,

a pilot relief-valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value corresponding to twice the maximum force permissible against said slave piston and automatically reducing said adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a spring adjustment for said valve, and a pressure connection from said flow line to said relief valve and in pressure cooperating relationship to the spring adjustment in said relief valve.

6. In combination with a component to be controlled,

and which is supported by series circuit connected hydraulic cylinder drive assemblies,

a three-way valve assembly comprising a valve housing component having a valve passageway therethrough and three ports flow connecting with said passagey,

flow connecting means connecting one of said valve ports to said series circuit between two of said cylinder drive assemblies,

flow connecting means connecting a second of said ports to a source of hydraulic pressure,

flow connecting means connecting a third of said ports to discharge,

a valve component in said housing adapted in one position to block flow through any of said ports and adapted when shifted in one direction to flow connect the first of said ports to the second of said ports, and when shifted in another direction, adapted to flow connect said first port to said third port,

means supporting one of said valve assembly components independently of the component to be controlled,

a tape-like element connected at one end to the other of said valve assembly components and extending across said controlled component along a path defined by spaced sheaves, and at its other end anchored to a fixed point independently of said controlled component,

spring biasing means normally urging said other valve assembly component toward fully open condition of said valve assembly,

means for adjusting said tape-like element against the action of said spring means to establish a neutral or closed condition of said valve assembly, and with said controlled component in a desired position, whereby upon angular deviation of said controlled component in one direction from its desired position, said valve assembly will adjust to connect said intermediate point of said series circuit to discharge, and upon angular deviation of said controlled component in the opposite direction from its desired position, said valve assembly will adjust to connect said intermediate point to such source of hydraulic power.

7. In combination with a component to be controlled,

and which is supported by series circuit connected hydraulic cylinder drive assemblies,

a three-way valve assembly comprising a valve housing component having a longitudinal valve passageway therethrough and three ports flow connecting with said passageway,

flow connecting means connecting one of said valve ports to said series circuit between two of said cylinder drive assemblies,

flow connecting means connecting a second of said ports to a source of hydraulic pressure,

flow connecting means connecting a third of said ports means supporting one of said valve assembly components independently of the component to be controlled,

a tape-like element connected at one end to the other of said valve assembly components and extending across said controlled component along a path defined by spaced sheaves, and at its other end anchored to a fixed point independently of said controlled component,

spring biasing means normally urging said other valve assembly component toward fully open condition of said valve assembly,

means for adjusting said tape-like element against the action of said spring means to establish a neutral or closed condition of said valve assembly, and with said controlled component in a desired position, whereby upon angular deviation of said controlled component in one direction from its desired position, 1

said valve assembly will adjust to connect said intermediate point of said series circuit to discharge, and upon angular deviation of said controlled component in the opposite direction from its desired position, said valve assembly will adjust to connect said intermediate point to such source of hydraulic power.

In combination With a component to be controlled,

and which is supported by series circuit connected hydraulic cylinder drive assemblies,

a three way valve assembly comprising a valve housing component having a longitudinal valve passageway therethrough and three ports flow connecting with said passageway,

flow connecting means connecting one of said valve ports to said series hydraulic circuit between two of said cylinder drive assemblies,

flow connecting means connecting a second of said ports to a source of hydraulic pressure,

flow connecting means connecting a third of said ports to discharge,

spool type valve coponent in said housing adapted in one position to block flow through any of said ports and adapted when shifted in one direction to flow connect the first of said ports to the second of said ports, and when shifted in another direction, adapted to flow connect said first port to said third port,

means supporting one of said valve assembly components independently of the component to be controlled,

a tape-like element connected at one end to the other of said valve assembly components and extending across said controlled component along a path defined by spaced sheaves, and at its other end anchored to a fixed point independently of said controlled component,

spring biasing means normally urging said other valve assembly component toward fully open condition of said valve assembly,

means for adjusting said tape-like element against the action of said spring means to establish a neutral or closed condition of said valve assembly, and with said controlled component in a desired position, whereby upon angular deviation of said controlled component in one direction from its desired position, said valve assembly will adjust to connect said inter- 14 j mediate point of said series circuit to discharge, and upon angular deviation of said controlled component in the opposite direction from its desired position, said valve assembly will adjust to connect said intermediate point to such source of hydraulic power,

and means responsive to loss of control by said tapelike element for rendering said series circuit connected cylinder drive assemblies inoperative.

9. In combination with a component to be controlled, and which is supported by series circuit connected hydraulic drive assemblies,

a three Way valve assembly comprising a valve housing component having a longitudinal valve passageway therethrough and three ports flow connecting with said passageway,

flow connecting means connecting one of said valve ports to said series hydraulic circuit between two of said cylinder drive assemblies,

flow connecting means connecting a second of said ports to a source of hydraulic pressure,

flow connecting means connecting a third of said ports to discharge,

a spool type valve component in said housing adapted in one position to block flow through any of said ports and adapted when shifted in one direction to flow connect the first of said ports to the second of said ports, and when shifted in another direction, adapted to flow connect said first port to said third port,

means supporting one of said valve asembly components independently of the component to be controlled,

a tape-like element connected at one end to the other of said valve assembly components and extending across said controlled component along a path defined by spaced sheaves, and at its other end anchored to a fixed point independently of said controlled component,

spring biasing means normally urging said other valve assembly component toward fully open condition of said valve assembly,

means for adjusting said tape-like element against the action of said spring means to establish a neutral or closed condition of said valve assembly, and with said controlled component in a desired position, whereby upon angular deviation of said controlled component in one direction from its desired position, said valve assembly will adjust to connect said intermediate point of said series circuit to discharge, and upon angular deviation of said controlled component in the opposite direction from its desired position, said valve assembly will adjust to connect said intermediate point to such source of hydraulic power,

and means responsive to loss of control by said tapelike element for rendering said series circuit connected cylinder drive assemblies inoperative, said means including a normally closed emergency stop switch in the resulting path of movement of said spring biased valve component,

said normally closed emergency stop switch being adapted to remove power from said series connected hydraulic drive assemblies.

10. In combination a press brake having a series hydraulic drive system for the ram of said press brake, said system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies, and

means for developing full load rating force intermediate said series connected cylinder drive assemblies While limiting maximum force to each of the pistons of said series connected cylinder drive assemblies to a value substantially less than the full load rating of said press brake.

11. In combination a press brake having a series hydraulic drive system for the ram of said press brake, said system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting maximum force to each of the pistons of said series connected cylinder drive assemblies to a value less than the full load rating of said press brake, said means including,

a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value corresponding to full rate load of said machine and automatically reducing the adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a valve, a spring adjustment for said valve, and a pressure connection from said flow line to said relief valve and in pressure cooperating relationship to the spring adjustment in said relief valve.

12. In combination a press brake having a series hydraulic drive system for the ram of said press brake, said system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose un derside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting maximum force to each of the pistons of said series connected cylinder drive assemblies to a value less than the full load rating of said press brake, said means including,

a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value corresponding to full rated load of said machine and automatically reducing the adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a spring adjustment for said relief valve, and a pressure connection from said flow line to said relief valve and in pressure cooperating relationship to the spring adjustment in said relief valve, and

means for stabilizing said ram against angular deviations from a desired position.

13. In combination a press brake having a series hydraulic drive system for the ram of said press brake, said system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting maximum force to each of the pistons of said series connected cylinder drive assemblies to a value of the order of half the full load rating of said press brake, said means including,

a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentioned relief valve to a pressure value corresponding to substantially twice the maximum force permissible against said slave piston and automatically reducing the adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a spring adjustment for said relief valve, and a pressure connection from said flow line to said relief valve and in pressure cooperating relationship to the spring adjustment in said relief valve,

means for stabilizing said ram against angular deviations from a desired position, said means including,

a valve assembly having a port, flow connected to the flow line between said pair of cylinder drive assemblies,

a port, flow connected to a source of pressure liquid,

a port, flow connected for discharge from said flow line, and

means coupling said ram and said valve assembly to counteract undesired deviations of said ram from a desired position.

14. In combination a press brake having a series hydraulic drive system for the ram of said press brake, said system comprising a pair of cylinder drive assemblies including a master drive assembly,

a slave drive assembly,

said master drive assembly having a piston whose underside area is equal to the top side area of the piston in said slave drive assembly,

a supply line to said master drive assembly,

a flow line from said master drive assembly to said slave drive assembly,

means for supplying liquid to said series hydraulic drive system to simultaneously drive the pistons of said cylinder drive assemblies,

means for limiting maximum force to each of the pistons of said series connected cylinder drive assemblies to a value of the order of half the full load rating of said press brake, said means including,

a flow connection from pump pressure to discharge,

a pilot relief valve in said flow connection adjusted to maximum permissible limit of force against the slave piston, and

a pilot connection exposed to system pressure developed against said slave piston,

a flow connection from said supply line to discharge,

a relief valve in said last mentioned flow connection,

means for adjusting said last mentinoned relief valve to a pressure value corresponding to twice the maximum force permissible against said slave piston and automatically reducing the adjustment to a pressure value corresponding to said maximum permissible slave piston force, with changes in work position, from a position of symmetry between said cylinder drive assemblies to a position substantially beneath said master drive assembly,

said means including a spring adjustment for said relief valve, and pressure connection from said flow line to said relief valve and in pressure cooperating relationship to the spring adjustment in said relief valve,

means for stabilizing said ram against angular deviations from a desired position, said means including,

a valve assembly having a port, flow connected to the flow line between said pair of cylinder drive assemblies,

a port, flow connected to a source of pressure liquid,

a port, flow connected for discharge from said flow line, and

means coupling said ram and said valve assembly to counteract undesired deviations of said ram from a desired position, and

means for hydraulically limiting the stroke of said pistons.

15. The method of operating a hydraulically powered press brake or like machine in which a ram is exposed to stationary position loading and the hydraulic drive for such ram involves cylinder drive assemblies connected in series with one drive assembly functioning as a master drive assembly and another as a slave drive assembly and the supply line to said master drive assembly includes a relief valve adjusted for opening at the full rated load capacity of said machine when the work on said machine is symmetrically positioned between said cylinder drive assemblies, said method comprising limiting the maximum permissible force on the piston of said slave drive assembly to a value less than the full rated load capacity of said machine, and

as one shifts the work on said machine for a symmetrical position between said cylinder drive assemblies to positions closer to said master cylinder drive assembly, gradually lowering the adjustment of said relief valve from its full rated load capacity adjustment to a value comparable to said maximum permissible force on said slave position.

16. The method of operating a hydraulically powered press brake or like machine in which a ram is exposed to stationary position loading and the hydraulic drive for such ram involves cylinder drive assemblies connected in series with one drive assembly functioning as a master drive assembly and another as a slave drive assembly and the supply line to said master drive assembly includes a relief valve normally adjusted for opening at the full rated loaded capacity of said machine when the work on said machine is symmetrically positioned between said cylinder drive assemblies, said method comprising limiting the maximum permissible force on the piston of said slave drive assembly to a value of the order of half the full rated load capacity of said machine, and

as one shifts the work on said machine from a symmetrical position between said cylinder drive assemblies to positions closer to said master cylinder drive assembly, gradually lower the adjustment of said relief valve from its full rated load capacity adjustment to a value of the order of half the full rated load capacity adjustment.

References Cited in the file of this patent UNITED STATES PATENTS 

10. IN COMBINATION A PRESS BRAKE HAVING A SERIES HYDRAULIC DRIVE SYSTEM FOR THE RAM OF SAID PRESS BRAKE, SAID SYSTEM COMPRISING A PAIR OF CYLINDER DRIVE ASSEMBLIES INCLUDING A MASTER DRIVE ASSEMBLY, A SLAVE DRIVE ASSEMBLY, A SUPPLY LINE TO SAID MASTER DRIVE ASSEMBLY, A FLOW LINE FROM SAID MASTER DRIVE ASSEMBLY TO SAID SLAVE DRIVE ASSEMBLY, MEANS FOR SUPPLYING LIQUID TO SAID SERIES HYDRAULIC DRIVE SYSTEM TO SIMULTANEOUSLY DRIVE THE PISTONS OF SAID CYLINDER DRIVE ASSEMBLIES, AND MEANS FOR DEVELOPING FULL LOAD RATING FORCE INTERMEDIATE SAID SERIES CONNECTED CYLINDER DRIVE ASSEMBLIES WHILE LIMITING MAXIMUM FORCE TO EACH OF THE PISTONS OF SAID SERIES CONNECTED CYLINDER DRIVE ASSEMBLIES TO A VALUE SUBSTANTIALLY LESS THAN THE FULL LOAD RATING OF SAID PRESS BRAKE. 